In Band 13 and Band 20 specified in the communications standard of Universal Mobile Telecommunications System (“UMTS”), downlink frequencies are set lower than uplink frequencies. There are cases where a sufficient amount of attenuation cannot be secured in a transmitting frequency band when a reception filter of an antenna duplexer corresponding to such a communications standard is constructed of a longitudinally-coupled acoustic wave filter.
FIG. 8 is a schematic diagram of conventional acoustic wave device 900A contrived to improve an attenuation characteristic of a longitudinally-coupled acoustic wave filter, as described in Japanese Patent Laid-Open Publication, No. 1993-136651. Acoustic wave device 900A includes longitudinally-coupled acoustic wave filters 901A, 902A and 903A that are connected in series. Acoustic wave device 900A has a large insertion loss in the pass band, and hence, is not preferable as a receiving filter of an antenna duplexer.
FIG. 9 is a schematic diagram of another conventional acoustic wave device 900B disclosed in Japanese Patent Laid-Open Publication, No. 1998-270982. Acoustic wave device 900B includes two longitudinally-coupled acoustic wave filters 901B and 902B connected via one-port resonator 903B. FIG. 10 is a schematic diagram of still another conventional acoustic wave device 900C disclosed in Japanese Patent Laid-Open Publication, No. 2000-349590. Acoustic wave device 900C includes two longitudinally-coupled acoustic wave filters 901C and 902C connected via two one-port resonators 903C and 904C having different anti-resonance frequencies. It is not possible to obtain a sufficient amount of attenuation for any of acoustic wave devices 900B and 900C in which two longitudinally-coupled acoustic wave filters are connected simply via one-port resonators.